Rigid starter bars are generally more desirable than flexible bars because they are inherently self-supporting and thus the support rolls and associated structure required for flexible bars can be momtted. Not only does this simplify the installation, it minimizes the equipment which would have to be maintained or replaced in the event of a catastrophic molten metal breakout from the mold.
A disadvantage of rigid bars is that they occupy a lot of space during storage in location already cramped with runout tables, platforms, overhead ranges and other equipment. This probe is addressed by flexible bars which may be stored in neither a flat configuration, or a curved configuration having a smaller radius of curvature than the casting train.
In U.S. No. 4,291,748 to Langner, it is proposed to combine the advantages of a rigid baer with those of a flexible bar by using a bar having a rigid potion disposed at the leading end adjacent the casting and a flexible portion at the tail end. The rigid portion is constructed from a single piece having a radius corresponding to that of the casting retain and has a length roughly equal to one-half the distance between the mold and the straightener. The flexible end comprises a number of solid long links each having a tongue and groove to cooperate with adjacent blocks and secured by through pins which permit limited, relative pivotal movement between the links so that the tail may be stored in a curved configuration to a radius which is smaller than that of the casting train.
While the proposal made in Langner to combine a rigid portion with a flexible portion is elegant, the structure described to achieve the claimed advantages has its own shortcomings. Because of its one piece construction, the rigid portion of the bar has to be manufactured within close tolerances in order for its shape to match the curvature of the casting arc.
In use, the rigid portion is subjected to pinch roll force in the straightener system and these tend to distort it geometry, and thus frequent reshaping or replacement of this component is required. Heat treatment to improve the properties of the material is not possible with the one piece construction because it would lead to unacceptable distortions.
The trailing flexible end of the bar has a tongue and groove construction typical of link-type bars and thus the typical problems encountered with this design, namely that the tongue and groove connections are reformed by frequent overrolling the straightener and a tendency for the connection to bind are also found in this portion of the starter bar. To remedy this situation by ample clearances causes unacceptable backlash problems of the starter bar system. Most systems built to this design have been replaced by entirely solid rigid dummy bars because it has been found impractical to maintain them.
An embodiment of a substantial solid rigid curved dummy bar is described in U.S. No. 3,930,533 to Rokop et al. This construction also suffers from the problem of distortion due to pinch roll forces and of space requirements for storage which Langner attempts to address.
It will be understood that the above-described problems become more pronounced in casting machines having larger casting radii.
An object of this invention to address the aforementioned problems in a starter bar having a rigid leading end and a flexible tail end.